1. Field of the Invention
This invention relates to an acceleration sensor used e.g. for detecting hand shake of a video camera, for detecting the movement in a virtual reality apparatus or for detecting the direction in a car navigation system and, more particularly, to a small-sized vibration type gyrosensor device having a cantilevered oscillator.
This application claims priority of Japanese Patent Application No. 2004-105885, filed on Mar. 31, 2004, the entirety of which is incorporated by reference herein.
2. Description of Related Art
As an acceleration sensor for household use, a so-called vibration type acceleration sensor in which a cantileverd oscillator is kept in a state of being oscillated at a preset resonance frequency, and in which the Corioris force produced under the effect of angular velocity is detected by e.g. a piezoelectric element, is in widespread use.
The vibration type acceleration sensor has various merits, such as a simple mechanism, short startup time, and low manufacturing costs, and is loaded e.g. on a video camera, a virtual reality device or a car navigation system, for use as a sensor for detecting the handshake, movement detection or direction detection.
The vibration type acceleration sensor is required to be of a small size and a high performance, in order to keep pace with the tendency towards a small size and a high performance of the electronic equipment on which to mount the gyrosensor. For example, with the tendency to providing the electronic equipment with multiple functions, there is raised a demand to loading the vibration type acceleration sensor, along with a variety of sensors used for other purposes, on a sole substrate, in order to reduce the overall size.
The vibration type gyrosensor suffers a problem that, since the piezoelectric material is sliced by mechanical machining, followed by shaping, in order to produce the oscillator, there is a limit imposed on the machining accuracy in reducing the size of the gyrosensor, with the result that the desired performance cannot be achieved.
Thus, a piezoelectric vibrational angular velocity meter, in which an oscillator is prepared by forming a thin film of a piezoelectric material on a single crystal silicon substrate for reducing the size, that is, a vibration type gyrosensor, has been devised (see for example Patent Publications 1 and 2). Such vibration type gyrosensor has also been devised which employs a cantilevered oscillator formed by a silicon machining process, and in which a driving electrode is mounted along the longitudinal direction of the oscillator, whilst a pair of detection electrodes are formed for sandwiching the driving electrode without contacting with the driving electrode (see for example Patent Publication 3).
Of these vibration type gyrosensors, it is required to detect the angular velocity with higher sensitivity.    [Patent Publication 1] Japanese Laid-open Patent Publication H8-261763    [Patent Publication 2] Japanese Laid-open Patent Publication H8-327364    [Patent Publication 3] Japanese Laid-open Patent Publication H7-113643